In this study we examined the expression of keratinocyte growth factor (KGF) mRNA and hepatocyte growth factor (HGF) mRNA in tissues obtained from spayed pigtailed monkeys on days 0, 1, 2, 3, 4, 5, 6 and 14 of the artificial menstrual cycle. Northern blot analysis of KGF and HGF mRNA in pigtailed monkeys revealed that the level of KGF mRNA in the endometrium was greatest on day 0 (after estradiol (E2) + progesterone (P) treatment) and decreased slowly after P withdrawal during days 0-6, a period known as the luteal-follicular transition (LFT). HGF mRNA was minimal on day 0 of the cycle and slowly increased during the LFT. KGF and HGF mRNAs in the oviduct and cervix of pigtailed monkeys were minimal after P treatment (day 0) and gradually increased after P withdrawal. These patterns of KGF and HGF mRNA expression were identical to the pattern seen in the rhesus monkey tract. However, we found that the reproductive tracts of pigtailed monkeys differed morphologically from the tract of rhesus monkeys, and that the tracts of pigtailed monkeys may be more like those of women. These differences include, 1) less cornification of the vagina after E2 treatment; 2) a more hypertrophied endometrium following P treatment; 3) less deciliation of the oviduct after P treatment; 4) more extensive shedding of the endometrium during menstruation; 5) evidence of retrograde transport of menstrual blood through the oviducts. Additional studies of pigtailed macaques are planned to document the value of this species for clinically relevant studies of reproduction.